Selective oxidation of substituted aromatic compounds using aldehyde-activated catalysts



2,673,217 COMPOUNDS D. c. HULL March 23, 1954 SELECTIVE OXIDATION OF SUBSTITUTED AROMATIC USING ALDEHYDE-ACTIVATED CATALYSTS Filed Sept. 21, 1951 PRESSURE CONTROL VA L V5 WATER FEED WATER scR UBBER PACKED WITH BE RL SADDLES CYCLONE SEPA RATOR OXIDIZED MATERIAL WIT HDRA WN FILTER PRODUCT RECEIVER 3! UR M Y .1 mm M Q mm M WWW 9 ms 6 w fi lv 4 4 I TE 3 0 ms. m0 an .Da GHull INVENTOR.

M /V\ WW1 vid GLACIAL ACETIC ACID z D \IE m mE N T M I m m 3 MT M m m m H m 2 m B C A EN R O E I P WM M M C m t|Y l m T A D ATTORNEYS Patented Mar. 23, 1954 SELECTIVE OXIDATION OF SUBSTITUTED AROMATIC COMPOUNDS USING ALDE- HYDE-ACTIVATED CATALYSTS David C. Hull, Longview, Tex assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application September 21, 1951, Serial No. 247,718

9 Claims.

This invention relates to a relatively low temperature liquid phase catalytic oxidation of certain substituted aromatic compound to obtain aromatic acids, aromatic lretones and various other oxidation products and more particularly to the oxidation, by means of aldehyde-activated metal catalysts, of substituted aromatic com pounds in which the substituent terminates in an alkyl radical under conditions in which cleavage of the aromatic ring s avoided.

This application is a continuation-impart of my application Serial No. 133,342, filed December 16, 1949, now abandoned.

Reference to the prior art, it is thought, shows that the various Workers in the oxidation field have overlooked the possibility of oxidizin substituted aromatic compounds such as mesitylene (1,3,5 trimethyl benzene) to uvitic acid (5 methyl benzene 1,3 dicarboxylic acid), beta-hydroxy ethyl benzene to benzoic acid, alpha-hydroxy ethy1 benzene to acetophenone and benzoic acid, allyl benzene to benzoic acid, cyclohexyl benzene to quinone and adipic acid, vinyl benzene (styrene) to benzoic acid, benzyl alcohol to benzoic acid, ethyl benzene to acetophenone, beta-methyl naphthalene to naphthoic acid and di-methyl substituted naphthalenes to the corresponding dibasic and monobasic acids. Furthermore, not only have none of the workers in the prior art recognized or applied the principle of aldehyde activation to such oxidations, but they also have operated under relatively high temperature conditions and obtained relatively low yields of their respective products.

The present invention has for its principal object to provide a. novel process for the economical and efiicient conversion of aromatic compounds to useful oxidation products as toluene acid, uvitic acid, and various other compounds. A still further object is to provide a process whereby aromatic compounds may be directly oxidized to the desired products without the necessity of going through intermediate steps. A still further object is to provide a process of carrying out such oxidations under relatively low temperature conditions at either ordinary or superatmospheric pressure so as to produce high yields of the desired oxidation products. Other objects will appear hereinafter.

These objects are accomplished by the following invention which, in its broader aspects, comprises first preparing an active or other suitable metal compound in an aliphatic acid, such as acetic acid, treating the solution with an oxygencontaining gas and simultaneously adding an ill aldehyde such as acetaldehyde, thereby to bring the metal catalyst into a highly active state, and thereafter feeding the substituted aromatic compounds, together with an excess of oxygen, into the catalyst solution while maintaining the catalyst in the solution in an active state by continuousl adding aldehyde. It will be observed, as will be apparent from the description set forth hereinafter in detail, that a relatively large amount of aldehyde is used, say of the order of about twice or more of the amount of aromatic compound being oxidized. Also relatively high catalyst concentrations and acid concentrations are usually employed. In accordance with the "invention, the original aromatic compound in shave set forth several of the preferred embodiments of my invention, but they ar included merely for purposes of illustration and not as a limitation thereof.

The single figure of the drawing attached hereto and forming a part of this application represents one form of apparatus which may be employed for the practice of my invention. Other suitable forms of apparatus which may be employed for the carrying out of such a process are illustrated in my patents for example, Patents 2,287,803 and 2,353,157.

My invention will be more fully understood by a preliminary discussion of th preparation and the composition of my improved catalyst solutions and the conditions under which my process is operated.

As indicated, I employ what I have described as an aldehyde-activated catalyst solution. Such a solution can appropriately be prepared, by dissolving a suitable catalyst metal or one: of its aliphatic acid-soluble oxides, salts or other compound in an aliphatic acid such as acetic, propionic or butyric acid. While in accordance with certain of the broader aspects of my invention, I may employ other metals which will produce metallic ions in solution, I have found cobalt to be an especially valuable catalyst, and, accordingly, my preferred embodiment and description herein is directed to my covalt type catalyst. However, in somewhat the same class with 00-- holmium, europium, erbium, gadolinium, thulium, terbium, dyprosium, and lutecium.

While in general I prefer to employ a single metal as the catalyst and in the form of one of 7 its oxides, salts or other compound which is easily soluble in the aliphatic acid selected as the solvent medium, I may, if desired, employ a plurality of such metals. For example, while I prefer to employ a solution of cobaltous acetate (CO(C2H302) 2.41120) in glacial acetic acid, I may employ a plurality of metals in the form of their acetates, propionates or butyrates, or in the form of oxides which form the corresponding aliphatic acid salts in the acid solution. Likewise, while I prefer to use acetic acid alone as the solvent, I may employ aliphatic acids such as acetic, propionic, butyric and the like, either singly or in various combinations one with another.

As to the matter of concentration, I may dissolve the catalyst metal in the acid to produce solutions containing anywhere from 2% to 8% of the metal, or metals, although, in general, I prefer to keep within the range of 5% to 8%. It will be noted that I employ a relatively high catalyst concentration as compared with certain prior art processes where the catalyst concentration is of the order of 0.1%. Likewise, although I prefer to dissolve the catalyst in anhydrous acid, a more dilute acid may be employed. In general, I have found that, in use, more satisfactory yields of product are'obtained if the acid concentration of the catalyst solution is at all times maintained at approximately 85%, or above. In other words, my acid concentration is preferably from 85% to substantially anhydrous.

Once the catalyst solution has been prepared as above described and charged into a suitable reaction vessel, it is brought into a highly active or activated condition by simultaneously feeding in an aliphatic aldehyde, such as acetaldehyde, and oxygen or an oxygen-containing gas at such a rate and at such a temperature as to cause the catalyst to become and remain active, a condition usually initially indicated by a change in color of the original solution. The oxygen feed is regulated to provide a slight excess of oxygen over and above that required for the oxidation reaction, such excess being indicated by the presence of a few per cent of oxygen in the gaseous efiluentsfrom the process. It will, of course, be understood that such matters as feed rates of aldehyde and oxygen, temperatures and the like, in general, have to be determined for each particular catalyst and with reference to the con pound to be oxidized. In the case of a cobalt catalyst in acetic acid, the original solution, which is pink, changes to green upon activation, indicating that the cobalt ions have changed from a lower to a higher state of valence, that is, from the cobaltous to the cobaltic state and that the solution is in the desired catalytically active condition.

While air is the most economical source of oxygen, I may employ any suitable oxygen-containing gas such as pure oxygen, ozone, or mixtures of such gases with inert gaseous diluents. Likewise, although I prefer to use acetaldehyde, I may employ other aliphatic aldehydes such as propionaldehyde, butyraldehyde and the like, all of which aldehydes may be employed singly or in various combinations one with another.

While in some cases the catalyst solution will become active merely upon introduction of the aldehyde and blowing with air or oxygen at ordinary atmospheric temperatures, it may be desirable to heat the solution moderately, say, to a temperature in the vicinity of 50-65? C. in order to initiate catalyst activity.

As to the matter of temperature, I may oxidize substituted aromatic compounds in accordance with my invention at a relatively low temperature within the range of 5 C. to 90 C. In general, high temperatures, that is, temperatures in excess of the boiling point of the solvent or product, are to be avoided in the interest of precluding degradation of reactants or products, or losses by evaporation, polymerization or like phenomena. In view of the fact that the oxidation reactions here involved are exothermic in character, it is usually necessary continuously to cool the reaction medium in order to keep the temperature within the desired limits, to prevent excessive loss of reactants by evaporation and to preclude the possibility of the reaction becoming too greatly accelerated. On the other hand, under certain circumstances it may be necessary actually to supply heat, as, for example, in the case of first starting the process, in order to initiate catalyst activity.

As to pressure, while I usually operate at atmospheric pressure, I may operate at pressures below atmospheric or as high as 2 to 10 atmospheres or more. It will, of course, be understood that the temperature and pressure may vary according to the requirements of the particular material undergoing oxidation, the rate of feed of the several reactants and with other variables, the control of which, in the light of the teachings herein, is within the skill of the trained chemist or chemical engineer.

It will, of course, be understood that in oxidizing substituted aromatic compounds in accordance with my invention the oxygen supplied by continuous introduction of air or other oxygencontaining gas, as explained above, is the fundamental source of oxygen for the oxidation reaction.

The reaction product or products will, of course, vary with the material undergoing oxidation. As indicated above, I have found that mesitylene (1,3,5-trimethyl benzene) may be converted by my process to uvitic acid (5 methyl benzene, 1,3 dicarboxylic acid), beta-hydroxy ethyl benzene to benzoic acid, alpha-hydroxy ethyl benzene to acetophenone and benzoic acid, allyl benzene to benzoic acid, cyclohexyl benzene to quinone and adipic acid, vinyl benzene (styrene) to benzoic'acid, benzyl alcohol to benzoic acid, ethyl benzene to acetophenone, betamethyl naphthalene to naphthoic acid and di- 'methyl substituted naphthalenes to the corresponding dibasic and monobasic acids. Substituted aromatic compounds wherein the substituent terminates in an alkyl group such as a methyl, exemplified by the xylenes may be oxidized by my process.

My invention will now be more clearly understood by reference to a practical operation which may be conveniently carried out in an apparatus such as that illustrated in the single figure of the drawing.

The numeral l designates an oxidation unit which may consist of a plurality of flanged stainless steel tubes of six-inch inside diameter and approximately ten feet long, or any other convenient size or proportions, superimposed one on top of the other and bolted together, the main sections being represented by numerals 2, 3, 4 and 5. Each section is provided with a suitable temperature-controlling means which may take the form of an internal centrally disposed stainless steel coil, such as coil 6 of section 5, of onehalf inch or other appropriate inside diameter, each coil being supplied with a temperaturecontrolling medium, such as water, or steam, as the situation may require, through inlet l and emerging therefrom through outlet 8. Each section is also supplied with a thermometer T, as shown, inserted through the wall of each section by means of a thermometer well (not shown).

The lowermost section of the oxidation unit consists of a tubular stainless steel member 9 of the same inside diameter as the upper sections of the unit, fianged at the top and closed at the bottom. To section 2 is connected inlet conduit ii), flow of liquid through which is controlled by valve ll. Connected into conduit is is valved aldehyde feed conduit l2 and another valved conduit 3 for supplying the material to be oxidized to the oxidation unit. While the valves in these feed lines may be so operated as to provide a regulated or metered fiow oi materials to the unit, a somewhat more convenient method is to provide rotameters or other metering devices for this purpose.

Section 9 has tapped into its lower closed end another inlet conduit it into which is connected air inlet conduit l5, fiow of air or other oxygen-- containing gas through which is controlled by valve l6. Conduit M is extended beyond its junction with conduit is as shown, the extension being equipped with a valve ii to provide a means for draining the unit when not in use or between successive runs.

A perforated diifusion plate is inserted and bolted in place between the lower flange of section 2 and the flanged top of bottom section El to provide a means of evenly distributing the liquidgaseous mixture which enters the bottom of the unit.

The topmost portion of the oxidation unit may conveniently comprise three sections, l8, l9 and 20, each of which is flanged and bolted together as previously described. A distributor plate, which may include a bubble cup and downcomer, is positioned between the upper flange of section 5 and the lower fiange of section It. To sections l8 and 59 there is connected a high-pressure sight glass 2! for indicating the level of liquid in the upper part of the unit.

The upper closed end of section 26 is provided with an outlet conduit 22 adapted to conduct vapors and gas evolved from the top of the unit to cyclone separator 23 where any entrained liquid is separated from the mixture and conveyed back into the upper part of the oxidation unit at section 18 through conduit 24, the latter being so formed at its end to provide a liquid seal in proximity to its junction with section iii.

Cyclone separator 23 is also provided with an outlet conduit 25 which conveys gaseous and vaporous materials to water-cooled condenser 26 of appropriate size and design, cooling medium for which is supplied through inlet 28 and emerges through outlet 27. Condenser 2G is also connected through conduit 29 and sight glass 30 to product receiver 3|, the latter also being provided with a sight glass 32 for indicating the level therein. The product receiver is also equipped with valved conduit 33 for withdrawing product therefrom as desired.

Vapors not condensed in condenser 25 may find their way in the direction indicated by the arrows, through conduits 34, 35, and 36 into the bottom of scrubber 31 which may take the form of a stainless steel tube of appropriate diameter packed with a liquid distributing material such as berl saddles or Raschig rings. Scrubber 31 is provided near its upper closed end with conduit 38 through which water is supplied, passing in countercurrent to the vapor-gas stream ascending in 31 and thereby dissolving out any portions of products or reactants which may have escaped entrapment in separator 23 or condenser 26.

The lower end of scrubber 3'! is connected, through conduit is to scrubber receiver 3! which may, like its counterpart 3i, be provided with a sight glass 32' for indicating the liquid level therein. Scrubber receiver 3! may be drained, when necessary,.through valve 33' to a recovery system.

crubber 3'! is also provided at its upper end with a gas outlet conduit 3? and pressure control valve 39, through which gas may escape to the atmosphere.

In order to recover the acid made from the oxidation of the substituted aromatic compounds, the catalyst solution is overflowed or withdrawn from the oxidation unit at a slow rate through conduit 39, valves fill or M to jacketed crystallizers 44 or 45 which may be provided with stirrers or agitators 42 and I3. Cboling medium is turned into the jackets of the crystallizers and the mixture is cooled to around 5 C. While crystallization is being carried out in one crystallizer, the other is being filled. When the crystallization is complete valve 44 or 5 is opened and the material is allowed to pass into filter as or to a centrifuge (not shown). The solid acid is removed from the filter or centrifuge and further purified. The filtrate, containing most of the catalyst in solution passes through conduit is to receiver 50 or 5|, from which it is pumped continuously by means of pump 53 through conduit 52 to the bottom of the oxidation unit. If the acid content of the catalyst has dropped below mentioned above, concentrated acid may be added, for example, to the materials in conduit 52 for raising the acid content to the desired range.

The operation of the apparatus when used to carry out the process of my invention will be apparent on inspection. In starting, oxidation unit 4 is filled somewhat less than full with catalyst solution, which may conveniently take the form of a 3% solution of cobaltous acetate in glacial acetic acid. Air valve It is opened slightly and aldehyde feed is put on the unit by opening the valve in feed line I2. It will, of course, be understood that a suitable temperature-controlling medium, such as water, is supplied to the several coils of the unit and that the thermometers are in place in the respective thermometer wells for taking readings of the temperature of the solution.

If the catalyst solution does not become active, as indicated by change in color from pink to green, after the elapse of several hours, it may,

be necessary to supply steam to the coils instead of cooling medium thus to raise the temperature to approximately 60 C. When the catalyst has become active, it is generally desirable to add more cobalt acetate to bring the concentration up to approximately 6%, thereby providing a catalyst concentration somewhat higher than the catalyst concentration used in certain prior art oxidation processes. The amount of catalyst dissolved in the original solution may vary, not only with the particular catalyst selected, but also with the temperature and various other conditions. Suffice it to say that between 2-6 per cent of the catalyst material is generally sufficient for effective operation provided that it is suitably activated with aldehyde, as has been described.

Once the catalyst has been activated, the material to be oxidized is introduced into the oxidation unit through conduit I3 and the aldehyde and air feeds are adjusted so as to provide'the proper proportion of each material to perform their respective functions. In general, the rate of aldehyde introduction will be controlled so as to maintain the catalyst at all times in an active condition, and, as will be apparent from the examples, which follow, substantial concentration of aldehyde is fed along with the aromatic compound being oxidized. That is, 2 supply an amount of aldehyde of the order or" at least as great as theamount of the aromatic compound and preferably at least twice or greater than the amount of the aromatic compound. The rate of oxygen feed preferably will be so regulated as to provide a slight excess of oxygen over and above that actually required for oxidation of the material being converted, as indicated by a few per cent of free oxygen in the effluents from the process.

The uncondensable gases and vapors are conveyed through conduits 4, and 36 into water scrubber 37, passing upwardly in counter-current to a stream of water. A part of the vaporized materials which have escaped condensation in condenser 26 are thus dissolved in the water and find their way to tank 3 l Non-condensable gases, such as carbon dioxide and nitrogen (from air, if air is used as the source of oxygen), emerges from the top of scrubber 31 through conduit 3'1 and eventually into the atmosphere through valve 39.

The product of the process, which may be in the form of a more or less dilute acid or other oxidation product, may be removed and conveyed to any desired concentration or purifying steps for conversion into the desired concentrated acid or other product. Likewise, the acid or other materials which have been scrubbed out of the vapor-gas stream passing through scrubber 3'! may be removed from scrubber receiver 3! through valved conduit 33 and treated in. any appropriate manner for recovery or" the dissolved materials.

As to the matter of temperature, I may conveniently carry out oxidations in accordance with my process, when operated at atmospheric pressure, within the range of C. to 90 G. Since the reactions involved are exothermic, it is generally necessary continuously to supply a cooling medium to the coils of the oxidation unit in order to maintain the temperature within the indicated limits. However, in some cases, pressures in excess of atmospheric will be desirable, for example, in order to prevent boiling away, either of the acetic or other aliphatic acid catalyst solvent or of the product of the reaction itself. It will be understood that valve 39" may be partially closed for maintaining the desired factors, in general pressures ranging from atmospheric to 10 atmospheres are those that I employ if I operate my process under pressure.

My invention will be more fully understood by reference to a number of specific examples illustrating conversions carried out in accordance therewith.

Example 1.--Oacidation of toluene to benzoic acid The oxidation unit was filled with a catalyst solution which comprised about 3% cobalt acetate in glacial acetic acid. Air was turned on and acetaldehyde feed started. The temperature at the start of the acetaldehyde feed was 30 C. After feeding the acetaldehyde for 1 hours, the temperature rose rapidly to 50 C. at which time cooling water was turned on and the temperature maintained between 50 and 60 C. during activation. After operating two hours in this manner more cobalt acetate was added until a total of 6% cobalt acetate was present in the catalyst. After three hours more operation after the fina1 addition of cobalt acetate, the catalyst solution was sufiiciently active to start full operation.

The temperature of the oxidation unit was regulated at 5ii C. and the feeds were adjusted so that the ratios were 20 mol per cent toluene and mol per cent acetaldehyde. The feed was continuous and over a 14 hour period, 39 pounds of acetaldehyde and 19 pounds of toluene were fed. It will be observed from the foregoing that the amount of aldehyde employed in my new process is substantially in excess of the amount of the aromatic compound, in this example toluene, being oxidized. During this time approximately 8 pounds of benzoic acid was re-.

crystallized out, and was then centrifuged to remove the crystals. The filtrate which contained most of the catalyst, was then returned to the unit. The benzoic acid was refined by sublimation.

Example II.--Owidation of ortho-rylene to ortho-tolu'ic acid An active catalyst was prepared as described in Example I. Ortho-xylene and acetaldehyde were fed to the unit continuously in the ratio of 15 mol per cent o-xylene and molper cent acetaldehyde. The temperature was maintained at 58-60". A total of 2368 parts of acetaldehyde and 1003 parts of o-xylene were fed to the unit giving 513 parts of o-toluic acid, representing a conversion of o-xylene to o-toluic acid of 37%. The o-toluic acid was recovered from the catalyst solution in a similar manner as described in Example I. Here again, it will be observed in my process that aldehyde in an amount several times the amount of the xylene being oxidized is used.

Example IIL-Oxidation of mesitylene to avitic acid After preparation of an active catalyst as previously described mesitylene was fed to the oxidation unit along with acetaldehyde. A total of 1197 parts of mesitylene were fed to the unit and a substantial amount (8513 parts) of acetaldehyde. lhe average temperature of the oxidation was 60 C., and the pressure was maintained at atmospheric. It was found that 374 parts of uvitic acid was made, representing a conversion of 20.8% of mesitylene to the acid. The uvitic acid was recovered by continuously removing the catalyst, cooling to crystallize the acid, centriiue ing or filtering and returning the filtrate as described in Example 1.

Example IV.-The oxidation of aceiopheaone to beazoic acid An active catalyst was prepared in the usual manner, then a mixture of 4000 parts acetaldehyde and 1200 parts acetophenone were fed to the oxidation unit while operating at atmospheric pressure and at a temperature of approximately 60 C. The operation was continuous and it was found that 243 parts of benzoic was made representing a conversion of 20%. The separation of the benzoic acid was accomplished in the usual manner.

Example V.-O;nidalion of beast/l alcohol to benzoic acid Benzyl alcohol and acetaldehyde were fed continuously to an oxidation unit in the ratio of mol per cent benzyl alcohol and 90 mol per cent acetaldehyde. After a total of 797 parts of benzyl alcohol and 2575 parts of acetaldehyde had been fed in, 559.4 parts of benzoic acid were recovered. The conversion of benzyl alcohol to benzoic acid was 63.17% with a yield of 80.15%. The temperature was maintained at 5060 C. and the pressure atmospheric.

Example VI.-O:cidation of allyl benzene to benzoic acid After activating a cobalt acetate solution, allyl benzene and acetaldehyde were fed into the unit in the ratio of 10 mol per cent allyl benzene and 90 mol per cent acetaldehyde. The temperature of oxidation was maintained at 60-'70 C. and the pressure atmospheric. After a total of 940 parts of allyl benzene and 3300 parts of acetaldehyde had been fed to the oxidation unit in a continuous manner it was found that 184 parts of benzoic acid was made. This represented a conversion of allyl benzene to benzoic acid of 19% with a yield of 85%. The benzoic acid was recovered from the catalyst solution as previously described.

Example VII.-O:cidation of vinyl benzene to beneoic acid An active catalyst was prepared, then 940 parts of vinyl benzene and 2900 parts of acetaldehyde were continuously fed into the oxidation unit with a temperature of 60-70" C. and at atmospheric pressure. Upon recovering the products it was found that 2'75 parts of benzoic acid was made representing a conversion of 25% of the vinyl benzene to benzoic acid. The yield was 85%.

As may be seen from the foregoing, I have provided a relatively low temperature process for the oxidation of aromatic compounds whereby the desired oxidation product exemplified by aromatic acids may be produced in substantial yields. It will be further observed that, in my process employing an aldehyde-activated catalyst, the catalyst concentration of two to six, or eight, per cent, for example, is somewhat higher than the catalyst concentration heretofore used in certain prior art oxidation processes. It will also be observed, as has been pointed out above, that in my process I also introduce, along with the aromatic compound to be oxidized, a content of aldehyde which is usually several times the amount of the aromatic compound.

It has been mentioned above that the relative- 1y low temperature liquid phase catalytic oxidation process of the invention is useful for the oxidation of certain substituted aromatic compounds in which the substituent terminates in an alkyl radical and that the conditions of the process of the invention are such that cleavage of the aromatic ring is avoided. Typical compounds which may be oxidized advantageously in accordance with the invention, as further noted above, include those having more than one aliphatic, e. g., alkyl or alkenyl chain on the benzene ring and those in which the chains themselves may have certain substituents. It is not intended, however, that the invention be limited to the specific compounds disclosed, for the invention is of a broader utility. For instance, the process is admirably adapted to the oxidation of polysubstituted aromatic compounds having various unafifected substituents. Thus, the process is suitable for conversion of intro-substituted alkylated aromatic compounds to the corresponding nitro-aromatic acids without oxidation of any but the alkyl portion of the molecule. For example, the following compound are representative of appropriate starting materials:

One such oxidation was carried out as follows:

Fifteen parts of 5-nitroacenaphthene were added in small increments over a period of 6 hours to a solution of 11 parts of cobaltous acetate and 150 parts of butyric acid in a turbomixer. A slow stream of oxygen was used as the oxidant at a temperature of 80 C. and a total of 40 parts of butyraldehyde were added over the 6 hour period to maintain the catalyst activity. After this, the reaction was continued together with relatively high temperatures. Such prior art type processes cause a more complex reaction mixture to be formed than produced in accordance with my invention.

By employing higher catalyst concentrations,

substantial amounts of aldehyde and relatively low temperatures, the process of the present invention permits considerably milder and more specific oxidation, with the beneficial result of higher conversion and yield than heretofore obtainable. In other words, since, by the process of the present invention it is possible to employ temperatures below 100", there is less breakdown of oxidation intermediates into carbon dioxide and by-products by the process of the instant invention, than in prior art processes necessitating the use of higher temperatures.

It is, therefore, believed that a new and improved process has been described in the above specification.

Having thus described my invention, what I claim is:

1. A relatively low temperature process for the direct oxidation of an aliphatic hydrocarbon substituted nitrobenzene wherein said aliphatic substituent has from one to three carbon "atoms, which comprises treating a solution of 2-8% metal ion in a lower aliphatic acid with an aldehyde and a gaseous oxidizing medium containing free oxygen to form an active catalyst solution, simultaneously introducing material amounts of the said aliphatic hydrocarbon substituted nitrobenzene and additional aldehyde into the solution, oxidizing the aliphatic hydrocarbon substituted nitrobenzene of the resultant solution of catalyst, aliphatic hydrocarbon substituted nitrobenzene and aldehyde by treating the solution with a gaseous oxidizing medium containing free oxygen in slight excess, maintaining the solution during the introduction of the oxidizing medium at a temperature within the range of 5 C.-90 C., the process being characterized in that the aforesaid aliphatic acid is of at least 85% concentration and the aforesaid additional aldehyde is substantially greater in amount than the aliphatic hydrocarbon substituted nitrobenzene being oxidized.

2. An improved process for the direct oxidation of substituted aromatic hydrocarbons from the group consisting of toluene, xylene, mesitylene, allyl benzene, cyclohexyl benzene, ethyl benzene, hydroxy ethyl benzene, methyl nitrobenzene, ethyl nitrobenzene, acetophenone, methyl naphthalene and nitroacenaphthene, which comprises treating a solution of 2-892 metal ion in a lower aliphatic acid with an aldehyde and a gaseous oxidizing medium containing free oxygen to form an active catalyst solution, simultaneously introducing material amounts of the substituted aromatic hydrocarbon and additional aldehyde into the solution, oxidizing the substituted aromatic hydrocarbon of the resulting solution of catalyst, substituted aromatic hydrocarbon and aldehyde by treating the solution with a gaseous oxidizing medium containing free oxygen in slight excess, maintaining the solution during the introduction of the oxidizing medium at a temperature within the range of 5 C. to 90 0., the process being characterized in that the aforesaid aliphatic acid is of at least 85% concentration and the aforesaid additional aldehyde is substantially greater in amount than the aromatic hydrocarbon being oxidized.

3. A process for the direct oxidation of toluene to benzoic acid which comprises treating a solution of a metal ion in a lower aliphatic acid with an aldehyde and a gaseous oxidizing medium to form a catalyst solution, simultaneously introducing material amounts of toluene and additional aldehyde into the solution, oxidizing the toluene content of the resulting solution of catalyst, toluene and aldehyde by treating the solution with a gaseous oxidizing medium, maintaining the solution during the introduction of the oxidizing medium at a temperature of between 5-90 C., and thereafter recovering the acid produced, the process being characterized in that the aforesaid aliphatic acid is of at least 85% concentration and the aforesaid additional aldehyde is substantially greater in amount than the aromatic hydrocarbon being oxidized.

4. A process for the direct oxidation of xylene to toluic acid which comprises treating a solution of a metal ion in a lower aliphatic acid with an aldehyde and a gaseous oxidizing medium to form a catalyst solution, simultaneously introducing material amounts of toluene and additional aldehyde into the solution, oxidizing the toluene content of the resulting solution of cata-- lyst, toluene and aldehyde by treating the solution with a gaseous oxidizing medium, maintaining the solution during the introduction of the oxidizing medium at a temperature of between 5-99 C., and thereafter recovering the acid produced, the process being characterized in that the aforesaid aliphatic acid is of at least 85% concentration and the aforesaid additional aldehyde is substantially greater in amount than the aromatic hydrocarbon being oxidized.

5. A process for the direct oxidation of mesitylene to uvitic acid which comprises treating a solution of a metal ion in a lower aliphatic acid with an aldehyde and a gaseous oxidizing medium to form a catalyst solution, simultaneously introducing material amounts of mesitylene and additional aldehyde into the solution, oxidizing the mesitylene content of the resulting solution of catalyst, mesitylene and aldehyde by treating the solution with a gaseous oxidizing medium, maintaining the solution during the introduction of the oxidizing medium at a temperature of between 5-90 C., and thereafter recovering the acid produced, the process being characterized in that the aforesaid aliphatic acid is of at least 85% concentration and the aforesaid additional aldehyde is substantially greater in amount than the aromatic hydrocarbon being oxidized.

6. A process for the direct oxidation of allyl benzene to benzoic acid which comprises treating a solution of a metal ion in a loweraliphatic acid with an aldehyde and a gaseous oxidizing medium to form a catalyst solution, simultaneously introducing material amounts of allyl benzene and additional aldehyde into the solution, oxidizing the allyl benzene content of the resulting solution of catalyst, allyl benzene and aldehyde by treating the solution with a gaseous oxidizing medium, maintaining the solution during the introduction of the oxidizing medium at a temperature of between -90 0., and thereafter recovering the acid produced, the process being characterized in that the aforesaid aliphatic acid is of at least 85% concentration and the aforesaid additional aldehyde is substantially greater in amount than the aromatic hydrocarbon being oxidized.

7. A process for the direct oxidation of orthoxylene to ortho-toluic acid which comprises treating a solution of from five percent to eight percent of an aliphatic acid-soluble-cobalt derivative in a lower aliphatic acid of a concentration of 85% to and including anhydrous acid with a lower aliphatic aldehyde and with a gaseous oxidizing medium for several hours to form an active catalyst solution, substantially continuously introducing material amounts of orthoxylene and additional aldehyde into the solution, the process being characterized in that the amount of said aldehyde introduced into the catalyst solution is at least twice the amount of the ortho-xylene continuously passed therethrough to be oxidized, oxidizing the ortho-Xylene content of the resulting solution of catalyst, ortho-xylene and aldehyde by treating the solution with air, maintaining the solution during the introduction of the air at a temperature of about 50-60 C. and thereafter recovering toluic acid produced.

8. A process for the direct oxidation of mesitylene to uvitic acid which comprises treating a solution of from 5% to 8% of an aliphatic acid soluble with cobalt derivative in a lower aliphatic acid of a concentration of 85% to and including anhydrous acid with both a lower aliphatic aldehyde and with a gaseous oxidizing medium containing free oxygen, said treating being for a period of several hours to form an active catalyst solution, substantially continuously introducing material amounts of mesitylene and additional aldehyde into the activated catalyst solution, the process being characterized in that an amount of said additional aldehyde introduced into the catalyst solution is at least twice the amount of the mesitylene introduced thereinto for oxidation, oxidizing the mesitylene content of the resultant solution of active catalyst, mesitylene, and aldehyde, by also substantially continuously introducing thereinto a gaseous oxidizing medium containing free oxygen, maintaining the solution during the introduction of the oxidizing medium at a temperature of about C. and thereafter recovering uvitic acid produced.

9. A relatively low temperature continuous process for the direct oxidation of substituted aromatic hydrocarbons consisting of aliphatic hydrocarbon substituted benzenes wherein said aliphatic substituent is composed of from one to three carbon atoms, which comprises treating a catalyst liquid made up of 28% of a metal ion in a lower aliphatic acid with a lower aliphatic aldehyde and air to form an active catalyst liquid, after the active catalyst liquid is prepared, substantially continuously introducing material amounts of the substituted aromatic hydrocarbon and additional lower aliphatic aldehyde into the catalyst liquid together with the simultaneous introduction of further air, oxidizing the substituted aromatic hydrocarbon in the cata-- lyst liquid by means of the aforesaid introduction of air, maintaining the catalyst liquid during the introduction of air at a temperature within the range of 5 C. to 90 C., the process being characterized in that the catalyst liquid is comprised of a lower aliphatic acid of at least concentration and that the aforesaid additional aldehyde is supplied to the catalyst liquid in an amount which is substantially greater than the amount of the substituted aromatic hydrocarbon being simultaneously supplied.

DAVID C. HULL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 780,404 Bazlen et al. Jan. 17, 1905 2,245,528 Loder June 10, 1941 2,302,462 Palmer et al. Nov. 17, 1942 2,479,067 Greshman Aug. 16, 1949 2,497,889 Hull Feb. 21, 1950 FOREIGN PATENTS Number Country Date 623,836 Great Britain May 24, 1949 

2. AN IMPROVED PROCESS FOR THE DIRECT OXIDATION OF SUBSTITUTED AROMATIC HYDROCARBONS FROM THE GROUP CONSISTING OF TOLUENE, XYLENE, MESITYLENE, ALLYL BENZENE, CYCLOHEXYL BENZENE, ETHYL BENZENE, HYDROXY ETHYL BENZENE, METHYL NITROBENZENE, ETHYL NITROBENZENE, ACETOPHENONE, METHYL NAPHTHALENE AND NITROACENAPHTHENE, WHICH COMPRISE TREATING A SOLUTION OF 2-8% METAL ION IN A LOWER ALIPHATIC ACID WITH AN ALDEHYDE AND A GESEOUS OXIDIZING MEDIUM CONTAINING FREE OXYGEN TO FORM AN ACTIVE CATALYST SOLUTION, SIMULTANEOUSLY INTRODUCING MATERIAL AMOUNTS OF THE SUBSTITUTED AROMATIC HYDROCARBON AND ADDITIONAL ALDEHYDE INTO THE SOLUTION, OXIDIZING THE SUBSTITUTED AROMATIC HYDROCARBON OF THE RESULTING SOLUTION OF CATALYST, SUBSTITUTED AROMATIC HYDROCARBON AND ALDEHYDE BY TREATING THE SOLUTION WITH A GASEOUS OXIDIZING MEDIUM CONTAINING FREE OXYGEN IN SLIGHT EXCESS, MAINTAINING THE SOLUTION DURING THE INTRODUCTION OF THE OXIDIZING MEDIUM AT A TEMPERATURE WITHIN THE RANGE OF 5* C. TO 90* C., THE PROCESS BEING CHARACTERIZED IN THAT THE AFORESAID ALIPHATIC ACID IS OF AT LEAST 85% CONCENTRATION AND THE AFORESAID ADDITIONAL ALDEHYDE IS SUBSTANTIALLY GREATER IN AMOUNT THAN THE AROMATIC HYDROCARBON BEING OXIDIZED. 